The glycine, the iminodiacetic acid (I.D.A.) and the nitrilotriacetic acid (N.T.A.), described in numerous patents, are widely used in different sectors. For example, glycine can be used as a nutrient and both I.D.A. and N.T.A. are used in the process of synthesizing herbicides, among other applications. Since these products have appeared on the market, a variety of ways of obtaining them have been described and patented.
The Japanese patent 53/7709 held by the Mitsui Toatsu Chemical Co. Ltd, describes a procedure for obtaining I.D.A. and N.T.A. through the oxidation of diethanolamine and triethanolamine respectively, with oxygen gas in a base aqueous solution, using a noble metal (Pt and Pd) as catalyst for the reaction. Although the acids mentioned can be obtained through this procedure, the yield obtained for both I.D.A. (69%) and N.T.A. (60%), is rather low, and there is the added drawback that the possible losses of the noble metal used as a catalyst make this process unprofitable from an economic point of view. On the other hand, it is a fact, recognised by experts in catalysis, that noble metal losses occur in catalytic processes both for acids and bases, through the solution of the metal in the reaction water, a complex process being required for their recovery, and that there are also losses when the above-mentioned catalysts are being handled. As a result, it is difficult to make this type of process profitable considering that the end-products are of little economic value.
So, it would be useful if a process existed through which glycine and the acids I.D.A. and N.T.A. could be obtained in such a state of purity and with sufficiently high yields resulting from oxidation of mono-, di- and triethanolamine, respectively, using a catalyst that was not a noble metal (e.g. Copper-Raney), that the aforementioned economic shortcomings would be reduced to a minimum.
Therefore, one of the aims of the invention is to provide a procedure for oxidizing mono-, di- and triethanolamine, in the presence of a Copper-Raney catalyst, which gives good yields in the reaction performance as well as minimizing cost of the catalyst when obtaining the end-product.
On the other hand, other Japanese patents held by Nippon Catalytic Chem. Ind., 60/78.948, 60/78.949, 60/97.945, 60/100.545 and 61/65.840, provide a procedure for obtaining glycine, I.D.A. and N.T.A. by oxidizing the mono-, di- and triethanolamine in a base aqueous solution using Copper-Raney as a catalyst, but with oxygen or gas that contains oxygen, obtained using a water decomposition reaction according to the following reaction diagrams, respectively: ##STR2## In this procedure calculating, for example theoretically, the heat of the combustion and reaction required to obtain the iminodiacetic acid, this would be 2,053 Kcal/Kg of I.D.A. and the amount of hydrogen produced would be around 0.061 Kg H.sub.2 /Kg of I.D.A. So, for a load of 13.5 Kg of I.D.A. produced in 4 hours using the above-mentioned Japanese patent no. 69/78,948, the amount of hydrogen released would be 0.81 Kg that, at 25.degree. C. and 1 atmosphere, would be equivalent to 41 liters of hydrogen per minute, and this would have to be allowed to leave the reaction so that it could be carried out at the pressure of 9 Kg/cm.sup.2 which is referred to in the patent. So, in order to adopt this procedure, it would be necessary to have fireproof installations, and to work in greater safety conditions due to the presence of the hydrogen, and furthermore, the amount of heat to be delivered would have a considerable effect on the final manufacturing cost of the end-products.
As a result of the aforementioned, a second aim of this invention is to provide a mono-, di- and triethanolamine oxidation procedure in the presence of a Copper-Raney catalyst, this type being the same as in the two previous procedures, but with the advantage of it not being necessary to carry out the procedure in fireproof installations, plus the additional advantages of notably reducing the safety conditions for the procedure and reducing to a minimum the heat expenses required to manufacture the desired compounds.
The two aims of the procedure adopted for this invention arise from the new technology for the manufacture of glycine, I.D.A. and N.T.A., which are carried out according to the following reaction diagrams: ##STR3## which are slightly exothermic reactions, without releasing hydrogen and carried out without the use of noble metals but with Copper-Raney as the catalyst.